Internal combustion engines utilize valve lifters that operate in conjunction with cams of a camshaft to reciprocate the lifters. Typically, as the camshaft rotates, the cams of the camshaft operatively engage an end of the valve lifter to reciprocate the valve lifters in an internal combustion engine. The valve lifters are located within cylindrical bores in an engine block. The engine block provides a travel passageway for each valve lifter and allows oil to lubricate each lifter assembly. Oil is directed to the valve bores by a straight and common transverse oil passageway that intersects the valve bores.
Various valve lifter designs have been developed for specific engine environments. Hydraulic valve lifter assemblies and solid lifters are typically used for engines having relatively low revolutions per minute. Rolier valve lifters, which utilize a roller to contact the cams of a camshaft, are typically used in engines having relatively high revolutions per minute. The use of a roller to contact the cams reduces wear and extends the useful life of both the valve lifter and the cams of the camshaft.
One problem associated with valve lifters is the need to provide oil to the lifters as they reciprocate within the valve bores and to the valve lifter rollers and cams of the camshaft as the lifters ride on the cams. When using roller valve lifters, it is important to provide sufficient oiling of the rollers and cams particularly at the point of contact. A known approach to increase the oiling of these areas is to provide an oil pressure feed groove on the valve lifter. This oil pressure feed groove is typically an annular groove on the circumference of the tappet body of the valve lifter. Oil enters the oil pressure feed groove from the common transverse oil passageway in the engine block that intersects the valve bores. As the valve lifter reciprocates within the engine, the oil pressure feed groove carries oil up and down the valve lifter bore and also directs oil towards the roller of the valve lifter that engages the cam. Although this method serves to provide some quantity of oil to the rollers and cams, in an engine having high revolutions per minute, there is a need to maximize the quantity of oil flowing to the rollers and cams to decrease roller and cam wear.
Another problem associated with engines having high revolutions per minute and using roller valve lifters is the need to supply adequate oil to the roller bearings of the valve lifter. Inadequate oiling of the roller bearing results in excessive wear and may lead to catastrophic failure of the bearing, and consequently failure of the entire engine. A known approach to oiling the roller bearings is to provide an oil feed slot or slots in the portion of the valve lifter that houses the roller. This oil feed slot directs any oil at the distal end of the valve lifter towards the shaft and bearings of the roller. While this method attempts to provide oil to the roller bearing, oil may not be present in this area or may be directed away from the shaft and bearing due to the rotation of the cam. Thus, there is a need to provide a positive flow of oil to the roller bearings to ensure oiling of the roller bearings.